Barnard's Loop

Barnard 's Loop ( catalog name Sh 2-276, German: Barnard's Loop ) is a large, O-shaped emission nebula in the constellation Orion. He belongs to a vast interstellar cloud in which, as can be detected by infrared astronomy, star formation takes place continuously.

The fog is in the form of an extended but faint loop that shines too weak to be visible with the naked eye. He is recognized only in very dark skies and with large astrographs. Barnard 's Loop takes place in a wide, north of Orion's belt arc starting from 10-15 ° diameter around the belt stars and the Orion nebula around the star are probably responsible for the ionization of the gas. Southward enough Barnard 's Loop almost to the bright star Rigel in the foot of Orion.

The widely extended H II region is 1500-1600 light-years away, measures about 300 light years in diameter and would fill in the infrared almost the whole constellation. In the dark with mist penetrated, glowing gas and molecular cloud (german giant molecular cloud GMC) will be formed in the next millions of years by shock waves and magnetic interactions numerous bright stars, forming a short-lived star clusters.

Explanatory models

The formation of Barnard's Loop was probably triggered by a supernova 2 million years ago, to the formation of some stars could go back in the constellations Fuhrmann and Aries. Other astronomers keep the fog because of its pale ring shape for direct remnant of a supernova, or cause the formation of its H II region on the solar wind of some young stars back because the Trapezium stars located approximately in the center of the arc.

It could also be the ionized inner surface of a much larger gas cloud. In any case makes this great " interstellar bubble" some interactions between interstellar medium and nearby stars clearly.

Observations in ultraviolet light show that Barnard 's Loop not only illuminates itself, but also in scattered starlight. As a reflection nebula its greatest intensity coincides with the spectra of young O and B stars in the Orion Nebula. Some parts of the reflection nebula measure almost 30 ° (?) In diameter, which they surpass the already large HII share by 4 times.

Related fog in the area

In nearby - just south of the left belt star Alnitak - is the famous Horsehead Nebula. He gets his outline by the head-shaped dark cloud right in front of emission nebula and is related to Barnard 's Loop.

Also the nearby Orion Nebula (M 42) is a birth place for young stars. The Hubble Space Telescope has discovered here numerous Protoplanetary discs, some of which may lead some to planet formation.

In the interior of Barnard 's Loop is another small nebulae find the right belt star. About 10 ° to the side of Orion is the roughly the same bright and also reddish, but smaller Rosette Nebula NGC 2237th

Discovery and visibility

The fog was discovered in 1895 by Edward Barnard at the Yerkes Observatory on a photographic plate, which was made with only about 20 cm large portrait camera.

The lighter parts of Barnard 's Loop has probably already seen William Herschel in 1786. As the fog already with telephoto lens from about 10 minutes exposure time is photographically recognizable, it requires visually in today's light pollution next to a bright telescope also a fog filter. Brighter areas in the loop then appear as diffuse background lights.

Pictures of Barnard's Loop

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